Meet Their Match in a Novel Bioherbicide
By Jan Suszkiw
July 6, 2001
Annual morningglories and other
broad-leaved weeds could meet their match in a novel bioherbicide that includes
weak or nonvirulent fungi and an oil emulsion,
Agricultural Research Service (ARS)
Use of the bioherbicide could offer a nature-based alternative to
conventional chemical controls--and the risks associated with applying them,
such as drift beyond crop fields and groundwater contamination--note ARS plant
pathologist Norman Schaad and retired ARS researcher Shaw-Ming Yang.
One bioherbicide ingredient is the saprophytic fungus Myrothecium
verrucaria. In nature, it survives by absorbing nutrients from decaying
plant matter. When mixed with oil, however, it can kill many common dicot weed
species, including annual morningglories, bermudagrass, pigweed and bindweed.
In early greenhouse studies, Yang showed that oil serves as both an
emulsifier that retains moisture and a synergist that enables the fungus to
kill weeds. Neither M. verrucaria or oil alone will damage plants, so
natural movement of the fungus to crops or other nontarget plants isnt
In test plots in Maryland, Louisiana, Mexico and France, the fungus killed
or damaged the weeds as effectively as the herbicides atrazine and 2,4-D. In
June 2000 trials on Houma, La., sugarcane plots, about 95 percent of
smallflower morningglory plants sprayed with the fungus died 4 days later,
versus 100 percent for those treated with atrazine. Rex Millhollon, a
collaborating scientist at ARS
Station in Houma, conducted the trials.
The team began experimenting with M. verrucaria in 1997. In 1998,
they received a patent covering use of weak or nonvirulent fungi in combination
with an adjuvant and oil emulsion as a broad-spectrum bioherbicide. The
technology is now available for licensing. Before commercialization is
possible, however, scientists must first determine whether this strain of the
fungus produces metabolic byproducts called trichothecenes that are dangerous
to humans and other animals. Dana Berner and assistant Larry Paxton are
investigating the possibility at ARS'
Foreign Disease-Weed Science
Laboratory in Fort Detrick, Md.
ARS is the U.S. Department of
Agriculture's principal scientific research arm.